The Echinoid Directory

Glossary

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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Glossary terms beginning with: M

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madrepores
Small perforations usually confined to genital plate 2 which mark the external opening to the water vascular system. These are also known as hydropores. (show image)
madreporite plate
The genital plate that lies at the apex of interambulacral zone 2 and which is pierced by madrepores. It is usually the largest of the genital plates. (show image)
mamelon
A rounded, ball-like articulation surface forming the top of a tubercle and the bearing surface on which the spine rests. The mamelon may be perforate (with a central pit) or imperforate (as in this picture). (show image)
marginal (fasciole)
A fasciole band that runs around the ambitus of the test, passing beneath the periproct at the posterior. (show image)
membranous gaps
Large gaps between plates of the corona that are filled with soft-tissue membranes in life. These are found only in the echinothurioids. (show image)
meridoplacous
An interambulacral plating arrangement in which the first (primordial) plate (red) is followed by a single sternal plate (2b: green). The second sternal plate (2a: green) is paired with the first episternal plate (3b: blue) (show image)
meridosternous
A meridoplacous plastron.
meridosternous
metaplacous
An interambulacral plating arrangement in which the sternal plates (purple) as well as the basicoronal plate (red) are arranged uniserially. (show image)
metasternous (plastron)
A metaplacous plastron (show image)
microcanal system
A system of fine, interconnected pore-space immediately beneath the outer plate surface (present in certain clypeasteroids and best observed in slightly abraided tests). (show image)
miliary granule
A microscopic knob-like projection from the plate surface that lacks a distinct mamelon but which supports a fine stalked pedicellaria or tiny spinelet. (show image)
milled ring
A small flange near the base of the spine marking the distalmost limit of muscle attachment onto the spine base. (show image)
monobasal (disc)
An apical disc with five ocular plates but only one genital plate (G2). This genital plate dominates. (show image)
monocyclic (disc)
An apical disc in which all of the ocular plates are in contact with the periproct, and separate adjacent genital plates. (show image)